The invention is particularly applicable to contact rails which may be at ground level or suspended at a height, for supplying electricity to handling equipment such as cranes, travelling cranes, container lifters, etc. Generally speaking such conductor rails comprise rigid section bars which serve both as a conductive path and as a guide path for a pickup friction shoe.
Expansion joints must be provided, and numerous solutions have been proposed for ensuring electrical continuity (i.e. pickup continuity) and mechanical continuity (i.e. guidance continuity) at said expansion joints.
One solution consists of providing an empty space between the rail components and in providing two friction shoes on a carriage so that one or other of the shoes is always in contact with the track on a rail even when the other shoe is over empty space, thereby ensuring continuity in electrical pickup when the carriage passes over an expansion joint. This solution is unsatisfactory, both technically and economically. In order to improve it, and in particular to avoid the shocks to which the shoes are subjected when they pass over the expansion joint gap, proposals have been made to provide a pickup track having a transition curve between two adjacent rail components, and to provide the carriage with two friction shoes capable of rocking relative to the carriage. The curved track then serves to raise one of the shoes from its initial position while the other shoe ensures electrical continuity, and the carriage passes more easily over the expansion joint. However, this complicates the pickup shoe assembly, thereby increasing manufacturing costs.
Other solutions have been directed towards the expansion joint between the free ends of two adjacent section bars, providing that the free ends remain in contact with each other in such a manner as to ensure electrical pickup continuity regardless of their relative longitudinal positions. Thus, for example, one proposal consists of providing a notch at the end of the conductor bar and extending halfway across the conductive path, enabling two half-section bars to run side-by-side over a transition zone, thereby providing pickup from both bars in common over said transition zone. A variant on the same principle is to provide a central slidably mounted fishplate which is preferably slidably received at both ends in the end portions of two adjacent conductor bars, thereby providing a relatively rigid transition zone over which electrical pickup continuity is ensured. These various solutions are illustrated. for example, in German published patent specification No. 2 159 087.
Such a solution is better than the previous solutions, but it still suffers drawbacks. The worst of these drawbacks is the loss of shoe guidance over the expansion joint. For example, if a V-shaped path is used to provide such guidance, the full V-shape is available only in the overlapping middle portion of the expansion joint, with each end of the expansion joint having a gap in one of the sides of the V. In particular, when a contact shoe passes over such an expansion joint it suffers shocks due to a gap first on one side and then on the other side of the V. These shocks increase the rate at which shoes wear, and the regular, repetitive nature of such shocks gives rise to fatigue in the shoe-supporting mechanisms.
The discontinuity due to the expansion joint cannot be eliminated since the length of the common pickup zone is a function of the differences observed between the minimum and the maximum temperatures in use and the linear expansion coefficients of the conductor bar components. Under all circumstances some kind of expansion joint gap must be provided. In order to provide mechanical continuity and in particular continuity of rigidity, it is necessary either to provide a system of side fishplates or else to provide a special connection between section bars to bridge the expansion joint. In spite of such techniques, lateral contact between the notched ends of the bar components is not always as good as is desirable.
Proposals have also been made to use provisional connection fittings between the section bars so as to facilitate transport operations. Such fittings must be removed before the bars are used as a contact rail; otherwise, there would not be an expansion joint between adjacent rail components. This solution is not reliable since there is always the risk that workmen might forget to remove a fitting.
A further attempt at reducing the effects of discontinuity between rail components is illustrated in French published patent specification 2 238 802 which describes a guide rail for air-cushioned vehicles including expansion joints comprising two vertical half-section parts having bevelled ends in order to provide improved thrust contact by providing a zig-zag transition zone.
Preferred embodiments of the present invention provide a conductor rail component having an expansion joint which avoids the above-mentioned drawbacks of the prior art, in which the expansion joint is effective for providing both electrical and mechanical continuity.
Preferred embodiments of the present inention also provide optimum guidance for a friction shoe as it passes over an expansion joint without generating unwanted shocks and/or noise.
Preferred embodiments of the invention also provide conductor rails of considerable length ready for installation which are not excessively expensive, and in particular which are considerably cheaper than existing solutions including a curved lift-off track.